Shallow, isolated slabs above Woods Lake

Location Name: 
Black Butte
Region: 
Carson Pass Area
Date and time of observation: 
Mon, 12/25/2017 - 12:00
Location Map: 
United States
38° 40' 53.022" N, 120° 1' 12.2376" W
See map: Google Maps
US


Red Flags: 
Whumphing noises, shooting cracks, or collapsing
Rapid warming
Terrain Trap
Observation made by: Professional Observer
Snowpit Observations
More detailed information about the snowpack: 

Warm day at Woods Lake with gloppy skinning conditions but still cold, dry snow on the most shaded slopes near and below treeline. Anything above treeline in this area is very wind affected.

Pic 1: The summer trail goes right through the middle of this small slope (out of frame on the upper right), and due to informal observations showing a very shallow slab over facets, I decided to try to avoid the trigger point by going below it. I still triggered a distinct collapse with a fracture line about 3 meters above me. 

Pic 2: Although most of Black Butte was wind scoured down to ice, there was a continuous patch of wind blown snow over facets. In this picture, I only dug down to a very firm ice layer; the snow depth was 90cm. 15cm of 4f hard slab over fist hard facets.

Pic 3: An ECT propagated on easy taps, and the slab dropped - shooting facets out from the failure plane. Location marked by pin drop.

One of my options for the day was to ski some of the steep NE aspects right above Woods Lake. While I didn't see evidence of the potential for large avalanches, this shallow slab-over-facet structure was enough to keep me away from the numerous terrain traps present there. 

Snowpack photos: 
Weather Observations
Blowing Snow: 
No
Cloud Cover: 
50% of the sky covered by clouds
Air temperature: 
Above Freezing
Wind Speed: 
Moderate
Precipitation: 
None
Air temperature trend: 
Warming
Wind Direction: 
West
Accumulation rate: 
None
More detailed information about the weather: 

Thin, high clouds